The internal erosion process and effects of undisturbed loess due to water infiltration
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Jianqi Zhuang I Jianbing Peng I Yi Zhu I Yanqiu Leng I Xinghua Zhu I Weiliang Huang
The internal erosion process and effects of undisturbed loess due to water infiltration
Abstract Internal erosion is a complex phenomenon that is one of the main risk factors to soil destruction. Its occurrence is mainly due to water infiltration and can cause slope instability. “Karst soil” is a type of loess with special soil and water sensitivity that makes it prone to landsliding. The processes of internal erosion include transport erosion and chemical dissolution, which strongly effect loess structure and strength. To reveal the internal processes and effects of the loess due to water infiltration, field investigations and indoor tests, including infiltration tests, undrained triaxial tests, particle analysis, chemical analysis, and scanning electron microscopy (SEM), were conducted. The results show that (1) the fine particles (clay and silt) and chemicals can move within the matrix of the macro-pores under seepage flow. The physical internal erosion is mainly due to fine particle migration out of the water and clay and silt particles, and the sample column settlement was 3.3 cm with a settlement ratio of 16.5%, which results in changes to the soil skeleton, increasing the porosity and infiltration rate of loess. (2) Chemical dissolution is also an important internal erosion process in loess, especially cations of Na, Mg, Ca, and K and anions of Cl, SO4, and CO3, which are mainly lost due to dissolution and flow out of with water and clay particles, resulting in altered physical characteristics of the soil. (3) Soil particles’ mitigation and chemical dissolution change the loess structure, leading to skeletal destruction and decreased peak strength and residual strength of the infiltrated sample to 7.75% and 8.13%, respectively. During internal erosion, physical fine particle migration and chemical dissolution are important for loess stability and loess slope susceptible to failure during water infiltration. Keywords Internal erosion . Water infiltration . Fine particle migration . Chemical dissolution . Loess Introduction Loess is a wind-blown, loosely consolidated deposit of fine sand and clay components which is distributed in the arid and semiarid regions in China. Chinese loess covers a total area of approximately 631,000 km2 and occupies 4.4% of the land in China (Liu 1985). The thickness of the loess deposits in this area vary from a few meters to more than 300 m (Derbyshire et al. 2000; Li et al. 2013). Loess has special characteristics of macro-pores, loose texture, and water sensitivity, which makes it prone to landsliding (Dijkstra et al. 1995; Derbyshire et al. 2000; Xu et al. 2007; Zhuang and Peng 2014; Zhuang et al. 2017). The initiation and development of landslides in Loess Plateaus is often a response to three necessary factors, including sufficient water (Zhuang et al. 2017; Peng et al. 2018a), considerably steep topography (Zhuang et al. 2016), and appropriate thickness (Derbyshire et al. 2000). Thick loess
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